The laser is a device which amplifies light and enables to generate a coherent monochromatic light having high intensity and excellent directionality. The dye laser is a liquid laser and is mainly constituted by an optical resonator comprising a transparent container retaining a solution of laser active dye and an energy source for pumping which is optically connected to the container. Usually, the dye solution is forcibly circulated during operation of laser for avoiding optical ununiformity of the solution.
As the energy source for pumping the dye laser, there are energy sources which generate high energy light, such as a discharge tube, a flash lamp, a gas laser (e.g., nitrogen laser, argon laser, etc.), a solid laser (e.g., Nd-YAG laser), and the like.
The dye molecules in the dye laser are excited to a high energy state by pumping, and in turn cause radiative transition. Of the thus generated lights, those which travel along the axis of the resonator are enclosed within the resonator for an enough long time to cause strong interaction with excited dye molecules. When the number of excited molecules exceeds the number of molecules in ground state, stimulated emission takes place. Thus, light is amplified in the resonator to generate laser light.
In comparison with solid lasers or gas lasers, dye lasers have the advantage that they have a large tunability of output wavelength. That is, since laser active dyes have some width as to fluorescence band, they permit to accurately tune output wavelength by using, for example, a prism or a diffraction grating.